The present invention relates to an apparatus and method for use in medical imaging. More particularly, the present invention relates to apparatus and method for positioning a patient and/or a secondary imaging coil inside a primary imaging coil.
In magnetic resonance imaging, a patient is placed inside a coil (the xe2x80x9cprimaryxe2x80x9d coil) which is large enough in diameter to receive the patient while he is lying prone on a table slidable into and out of the coil. A selected portion of the patient is then imaged by the use of electromagnetic radiation from the primary coil.
It is known to place smaller coils, called surface or volume coils, in close proximity to the specific part of the patient to be imaged, such as the neck, spine, or knee. These coils, referred to herein as secondary coils, are used to increase resolution by having a coil closer to the part to be imaged. It is essential to place the secondary coil in a particular orientation relative to the electromagnetic field generated by the primary coil.
Current imaging systems can only take images while a patient is in one particular position. One known device allows the patient to move his knee joint to different selected positions while the patient is in the primary coil. This device requires the patient to lie face down in the primary coil, which is extremely uncomfortable for the extended period of time required to image properly, especially in the close, almost claustrophobic confines of a primary MRI coil.
The present invention is an apparatus and method for use in medical imaging. The present invention provides a system to simulate within an imaging coil normal movements of body parts such as joints, and to improve imaging of soft tissue and bony parts as compared to a static system in which images are taken of a joint in only one position.
In accordance with a first aspect of the present invention, there is provided controlled motion of an extremity, while in an imaging coil, either patient directed or operator directed. A joint or body part is moved into various positions in multiple planes within its range of motion while a series of images are taken of the joint in the different positions. These individual images may then be collated into a cine format to effectively show the joint in motion. Thus, the present invention allows for studying a joint in motion and also allows for studying a joint or other body part at any positions within its range of motion allowable within the confines of the primary coil.
In accordance with a second aspect of the present invention, a surface or volume coil (referred to herein as a secondary coil) is coupled for movement with the joint or body part. The secondary coil is maintained in the proper spatial relationship with the primary coil""s electromagnetic field. Keeping the secondary coil as close as possible to the joint or tissue being imaged, while moving the joint or body part, provides greatly enhanced resolution and more detail in the final image.
Thus, to illustrate these first two aspects of the invention in knee imaging, the knee is fixed by holding the upper and lower legs with cuffs and a secondary coil is placed around the knee itself. The knee is then imaged at 0xc2x0 by using the primary and secondary coils. The knee is then flexed (either by the patient or the operator), and the secondary coil moves with the knee. The knee is progressively moved through various positions within its range of motion as limited only by the size of the primary coil. Images are taken at each position. The images may then be collated and shown in sequence to visualize the movement of the knee joint, or may be studied individually to study the joint at each position.
Similar systems are available for other joints, the back, neck, etc. These systems all are preferably provided as mechanisms usable with existing imaging tables to reduce cost. Alternatively, some of these may be built into a new imaging table.
Coupling a surface coil for movement with the extremity provides the necessary detail in the images, even with a larger primary coil, which is not available with present systems. Accordingly, it is possible to use a larger diameter primary coil, allowing this increased range of movement, without the degradation in image quality which would be expected from the increased coil size. For example, the knee could be flexed through its entire range of motion to allow optimum imaging of the knee joint. This is currently impossible with the known small primary coils which only allow about 50xc2x0 of flexion.
In accordance with another aspect of the present invention, traction is applied to a joint being imaged, in order to load the joint. This can simulate normal loading of a joint. Distracting a joint can also allow a better view of the parts of the joint and thus an increased imaging benefit. It can also allow simulation of normal loading of a joint, such as when carrying a heavy object or performing an athletic or work-related task. This feature is not available with present imaging apparatus. Traction can also be applied to a joint being imaged when the joint is in various positions, to simulate normal loading of a joint within its range of motion. Again, this feature is not available with present imaging apparatus.